Renal acid-base regulation is the kidney's excretion of the daily non-volatile (fixed) acid load and reabsorption of filtered bicarbonate, keeping net acid excretion equal to net non-volatile acid production.
Filtered HCO3− load is about 4300 meq/day versus a non-volatile acid load of only about 80 meq/day; almost all filtered HCO3− is normally reabsorbed, so urine is normally mildly acidic.
Factors Influencing Acidification of Urine
Four factors determine urinary acidification: renal acid excretion, renal HCO3− reabsorption, acid-base status of the body, and other (mainly hormonal) factors.